#microsecond  one millionth of a second; one thousandth of a millisecond
  supertype:  #time_unit__unit_of_time  a unit for measuring time periods
  part of:  #millisecond
  part:  #nanosecond  one billionth of a second; one thousandth of a microsecond
     part:  #picosecond  one trillionth of a second; one thousandth of a nanosecond
        part:  #femtosecond  one quadrillionth of a second; one thousandth of a nanosecond
           part:  #attosecond  one quintillionth of a second; one thousandth of a femtosecond

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